1. Field of the invention
The present invention relates to a reed switch glass tube.
2. Description of Related Art
A reed switch comprises a contact point composed of opposed magnetic wire rods, and a glass tube for encapsulating the magnetic wire rods, which opens and closes the contact point by providing a magnetic field from the outside of the glass tube. Encapsulation of the magnetic wire rods into the glass tube is performed by inserting the magnetic wire rods into the glass tube under inert gas, reducing gas or under vacuum and softening by heating both end parts of the glass tube to be sealed.
When end parts of the reed switch glass tube have sharp corners and fine cracks, there are problems that the end parts of the glass tube are chipped and cracked typically during transport and shards thereof are mixed into the glass tube at the time of an encapsulation process. Therefore, glazing treatment to carry out rounding processing by heating the end parts of the glass tube with a burner to be softened has been conventionally performed.
However, in recent years, as an electron device has been downsized and light-weighted, a reed switch glass tube has been more and more decreased in diameter, thickness, and length. Typically, a minute reed switch glass tube having an outer diameter of 1.3 mm, a thickness of 0.2 mm, and a length of 3.1 mm had a problem that it was not possible to prevent, for example, chipping and cracking of end parts of the glass tube at the time of rounding processing by burner heating.
Until now, a technique for rounding end parts of the glass plate by the irradiation of laser light to a side of the glass plate is known (for example, Japanese Unexamined Patent Application Publication Nos. JP 2000-344551 A and JP 10-111497 A). This technique is, however, to round the glass plate by moving laser beams along the side of the glass tube. Therefore, when this technique was adopted to a minute reed switch glass tube, irregularity caused by a beam trajectory occurs on end faces of the glass tube. As a result, irregularity involves at the time of the encapsulation process, which causes generation of bubbles.